This application is directed to coating systems for applying labels to bottles. More particularly, this application is directed to heat-activatable, alkali-removable labelling systems formed from blends of high acid acrylic resins. The labels produced can be rapidly and completely removed in an environmentally friendly manner by heated aqueous alkaline solutions.
With the increasing emphasis on environmental protection, reduction of landfill disposal areas, and the economic advantages of recycling containers, there is interest in environmentally friendly labelling systems, especially ones where labels are removable in aqueous alkaline solutions. Known alkali-removable labelling systems have been formulated from alkaline solutions of casein, which systems have the disadvantages of degradation and discoloration upon exposure conditions of heat and aging. Furthermore, such systems are not thermoplastic, a property that necessitates application of label adhesives prepared for these compositions by direct gluing rather than by melting and heat activation.
A further deficiency in such known labelling systems has been the slow and incomplete removal of labels and label adhesives from the containers to which they have been attached. Also, in the case of heat-transferred xe2x80x9cpaperlessxe2x80x9d labels, the alkali-removable protective top coatings have exhibited poor visual appearance resulting from cracking on aging and developing surface scratches from abrasion encountered during friction due to the containers being in close contact while moving on the production line.
Thus, there is a need for better labelling systems in which labels can be rapidly and completely removed.
It is an object of the invention to provide an environmentally friendly labelling system.
It is also an object of the invention to provide a heat-activatable, alkali-removable labelling system.
It is a further object of the invention to provide a method of producing abrasion-resistant, protective topcoats, inks, and heat-activatable adhesive formulations that produce non-hazing, clear, glossy films under conditions of pasteurization and immersion in ice water.
These and other objects of the invention will become more apparent from the discussion below.
The current invention achieves the desired characteristics of alkali-removability, heat activation, and abrasion resistance by utilizing solutions of blends of high acid acrylic resins with other harder acrylic resins thereby resulting in formulations low enough in viscosity for application by flexographic or gravure coaters and presses. The dried films of these products have excellent interlayer adhesion, and, in the case of the adhesive coating, sufficiently low softening point, high wet tack, non-blocking in the dried film, and provide excellent adhesion to plastic, glass, and metal containers.
According to a first embodiment of the invention, a heat-transfer label is particularly well-suited for use on silane-treated glass containers of the type that are subjected to pasteurization conditions, regardless of whether the glass containers have previously been pre-treated with polyethylene, oleic acid, stearate or the like. The heat-transfer label comprises (a) a support portion comprising a sheet of paper overcoated with a release layer of polyethylene and (b) a transfer portion over said support portion for transfer of the transfer portion from the support portion to an article upon application of heat to the support portion while the transfer portion is placed into contact with the article. The transfer portion comprises (i) an optionally alkali-removable protective lacquer layer, (ii) an optionally alkali-removable ink layer over said protective lacquer layer; and (iii) an alkali-removable, heat-activatable adhesive layer over said ink layer. Preferably the adhesive layer comprises an adhesive of the type present in a solvent- or water-based adhesive form or in a water-based adhesive dispersion. Each layer comprises one or more acrylic resins.
In a second embodiment of the invention the heat-transfer label comprises (i) an optional, optionally alkali-removable protective lacquer layer, (ii) an optionally alkali-removable ink layer over said protective lacquer layer, (iii) a substrate, and (iv) an alkali-removable, heat-activatable adhesive layer.
According to another aspect of the invention, the heat-transfer label is particularly well-suited for use on aluminum cans that have been treated with a highly-lubricating acrylic coating or varnish of the type used to prevent scratching and abrasion of such cans (said varnish either being used alone or in combination with a white ink), said heat-transfer label comprising (a) a support portion comprising a sheet of paper overcoated with a release layer of polyethylene and (b) a transfer portion over said support portion for transfer of the transfer portion from the support portion to an article upon application of heat to the support portion while the transfer portion is placed into contact with the article.
In addition to being directed to the above-described heat-transfer portion of the heat-transfer labels, as well as to the adhesive compositions used to form the adhesive layers of the heat-transfer labels, the invention is directed to methods for forming the adhesive layers with the aforementioned adhesive compositions, to the adhesive layers formed using the foregoing adhesive compositions, and to methods of labelling surfaces with the above-described heat-transfer labels.
It is to be understood that certain terms used herein, such as xe2x80x9conxe2x80x9d or xe2x80x9coverxe2x80x9d, when used to denote the relative positions of two or more layers of a heat-transfer label, are primarily used to denote such relative positions in the context of the way in which those layers are situated prior to transfer of the transfer portion of the label to an article since, after transfer, the arrangement of layers is inverted as those layers which were furthest removed from the associated support sheet are now closest to the labelled article.
The current invention achieves the desired characteristics of alkali-removability, heat activation, and abrasion resistance by utilizing solutions of high acid acrylic resins and/or blends with other harder acrylic resins thereby resulting in formulations low enough in viscosity for application by flexographic or gravure coaters and presses. The dried films of these products have excellent interlayer adhesion, and, in the case of the adhesive coating, sufficiently low softening point, high wet tack, non-blocking in the dried film, and provide excellent adhesion to plastic, glass, and metal containers.